The present invention relates generally to a hermetic scroll-type compressor including intermeshing fixed and orbiting scroll members and, more particularly, to such a compressor having a compliance mechanism that acts on the orbiting scroll member to bias it toward the fixed scroll member for proper mating and sealing therebetween.
A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port, thereby conveying and compressing the refrigerant fluid.
It is generally believed that the scroll-type compressor could potentially offer quiet, efficient, and low-maintenance operation in a variety of refrigeration system applications. However, several design problems persist that have prevented the scroll compressor from achieving wide market acceptance and commercial success. For instance, during compressor operation, the pressure of compressed refrigerant at the interface between the scroll members tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face surface of the opposite scroll member. Such leakage causes reduced compressor operating efficiency and, in extreme cases, can result in an inability of the compressor to operate.
Leakage at the tip-to-face interface between scroll members during compressor operation can also be caused by a tilting and/or wobbling motion of the orbiting scroll member. This tilting motion is the result of overturning moments generated by forces acting on the orbiting scroll at axially spaced locations thereof. Specifically, the drive force imparted by the crankshaft to the drive hub of the orbiting scroll is spaced axially from forces acting on the scroll wrap due to pressure, inertia, and friction. The overturning moment acting on the orbiting scroll member causes it to orbit in a slightly tilted condition so that the lower surface of the plate portion of the orbiting scroll is inclined upwardly in the direction of the orbiting motion. Wobbling motion of the orbiting scroll may result from the interaction between convex mating surfaces, particularly during the initial run-in period of the compressor. For instance, the mating wrap tip surface of one scroll member and face plate of the other scroll member may exhibit respective convex shapes due to machining variations and/or pressure and heat distortion during compressor operation. This creates a high contact point between the scroll members, about which the orbiting scroll has a tendency to wobble until the parts wear in. The wobbling perturbation occurs on top of the tilted orbiting motion described above.
Efforts to counteract the separating force applied to the scroll members during compressor operation, and thereby minimize the aforementioned leakage, have resulted in the development of a variety of prior art axial compliance schemes. In a compressor in which the back side of the orbiting scroll member is exposed to suction pressure, it is known to axially preload the scroll members toward each other with a force sufficient to resist the dynamic separating force. However, this approach results in high initial frictional forces between the scroll members and/or bearings when the compressor is at rest, thereby causing difficulty during compressor startup and subsequent increased power consumption. Another approach is to assure close manufacturing tolerances for component parts and have the separating force borne by a thrust bearing or surface. This requires an expensive thrust bearing, and involves high manufacturing costs in maintaining close machining tolerances.
In a compressor having a pressurized, or "high side", housing, discharge pressure has been used on the back side of the orbiting scroll member to create a compliance force to oppose the separating force. Problems associated with this arrangement include too great an upward force on the orbiting scroll member, thereby promoting rapid wear of the scroll wraps and faces and associated power losses.
In recognition of the aforementioned problems associated with axial compliance mechanisms using either suction pressure or discharge pressure, several prior art compressor designs have utilized a combination of gaseous refrigerant at suction pressure and gaseous refrigerant at discharge pressure. For instance, it is known to expose respective areas on the backside of an axially movable fixed or orbiting scroll member to the two different pressures in order to achieve a net desired force. In such compressor designs, various seal means are utilized to separate the respective gaseous pressure regions and to compensate for axial movement of the scroll member.
In another type of axial compliance mechanism, an intermediate pressure chamber is provided behind the orbiting scroll member, whereby the intermediate pressure creates an upward force to oppose the separating force. Such a design recognizes the problems associated with the use of suction pressure or discharge pressure alone, and obviates the need for sealing between respective areas of each. Such a leak results in less efficient operating conditions for the compressor.
Still another axial compliance mechanism for a scroll compressor involves exposing a radially inner portion of the orbiting scroll member bottom surface to oil at discharge pressure, and a radially outer portion to refrigerant fluid at suction pressure. The regions are sealingly separated by a flexible annular seal element that is disposed between the orbiting scroll member bottom surface and a rotating thrust surface comprising a radially extending plate portion of a driven crankshaft.
The present invention is directed to overcoming the aforementioned problems associated with scroll-type compressors, wherein it is desired to provide an axial compliance mechanism that helps to prevent leakage between the interfitting scroll members caused by axial separation therebetween and wobbling/tilting motion of the orbiting scroll member.